1. Field of the Invention
The present invention relates to a preferably integrated circuit configuration for the actuation of power switches disposed in bridge circuit topology as well as an associated method. More specifically, the present invention relates to a circuit configuration wherein, such bridge configurations of power switches are semi-, H- (two-phase), or as three-phase bridge circuits, the single phase semibridge representing the basic module of such electronic power circuits. In this configuration a semibridge circuit, two power switches, a first, so-called TOP switch, and a second, so-called BOT switch, are connected in series. Preferably, such a semibridge is connected to a direct current link and the center tapping is typically connected to a load.
2. Description of the Related Art
The related art involves a circuit configuration wherein when the power switches are implemented as a power semiconductor component or as a multiplicity of identical series- or parallel-connected power semiconductor components, an actuation circuit is necessary for the actuation of the power switches. Within the related art such actuation circuits are comprised of several subcircuits or function blocks. The actuation signal from a superordinate control is processed in a first subcircuit of a primary side, and, via further components, supplied to the driver circuits, the secondary sides and lastly to the control input of the particular power switch.
In semibridge configurations with higher link voltages, for example greater than 50 V, the primary side, in potential/electrical terms, is isolated from the secondary side for the processing of the control signals, since the power switches, at least the TOP switch of the semibridge, during operation are not at a constant potential and consequently the isolation in terms of voltage is unavoidable.
This isolation, according to related art takes place for example by means of isolating transformers, optocouplers, for example optical wave guides. This electrical isolation, is at least carried out for the TOP switch, but at higher powers also for the BOT switch due to a possible breaking of the ground reference potential during the switching.
Also known are integrated circuit configurations for power switches of voltage classes up to 600 V or 1200 V, which forgo the use of external electrical isolation. In these monolithically integrated circuits, according to related art, so-called level shifters are utilized, at least for the TOP switch. These electronic components and techniques for isolation consequently overcome the potential difference of the primary side with respect to the secondary side.
As background, and referring now to FIGS. 1 and 2, in the actuation of power semiconductor components 50, 52, such as for example IGBTs (Insulated Gate Bipolar Transistor) with antiparallel connected free-wheeling diode, in a circuit configuration in bridge topology, due to the voltage difference between superordinate control 10, for example in the form of a microcontroller 10, and the primary side 20 of the circuit configuration on the one hand, and the secondary side 30, 32 of the circuit configuration and the power semiconductor component 50, 52 on the other hand, a detrimental isolation of the potential is required. According to prior art, various feasibilities for potential isolation are known, for example transformers, optocouplers, optical wave guides or electronic components with appropriate electrical strength.
Specifically in FIG. 1, in the monolithic integration of primary side 20 and secondary side 30 of a circuit configuration 100 for actuating power semiconductor switches 50, 52, level shifters 44 are frequently utilized for the transmission of control signals from the primary side 20 to the secondary side.
With the components for the potential isolation, switch-on and switch-off signals can be transmitted from the primary side 20, (low voltage side) to the secondary side 30, (high voltage side). However, essential for the trouble-free operation of an electronic power system is the primary-side information about operating states of the secondary side 30, for example information about the concrete switched states of the TOP and of the BOT switch.
Specifically in FIG. 2, shown is a known topology of a monolithically integrated level shifter, here with an nMOS high-voltage transistor 430 with a blocking capacity corresponding to the maximal potential difference between primary 20 and secondary side 30. The actuation of the secondary side takes place from the primary side. As soon as the primary side 20 switches on the high-voltage transistor 430, a cross current (lq) flows between the supply voltage (Vs) of the secondary side and the ground reference potential of the primary side 20. This current flow (lq) is detected on the secondary side and converted into a signal to be processed further.
The level shifter 44 is controlled through the input signal (Sin). For this purpose, this signal is preferably preamplified and applied at the control input of a low-voltage transistor 432. As long as this low-voltage transistor 432 is open, the potential of the supply voltage (Vp) of the primary side is connected to the “source” of the high-voltage transistor 430. Since the “gate” of the high-voltage transistor 430 is also connected to the supply voltage (Vp) of the primary side 20, the entire offset voltage between primary side and secondary side falls across the high-voltage transistor 430. If the low-voltage transistor 432 is switched on, the potential at the source of the high-voltage transistor 430 falls and a cross current (lq) starts to flow. However, this current is limited by the counter-coupling resistor 424. The cross current (lq) consequently conveys the switching signal of the primary side to the secondary side thereby that here the voltage drop across the resistor 420 is interpreted. In the stationary state, in the presence of an input signal (Sin) “low”, this circuit does not consume any energy with the exception of the negligible leakage current of the high-voltage transistor 430. The signal deviation on the secondary side is limited through the Zener diode 410. Together with the resistor 424, the primary-side series connection of Zener diodes 412 protects the low-voltage transistor 432 against loading by transient overvoltages.
Due to the clamping on the secondary side and the current limitation across emitter counter coupling, the cross current (lq) during the switch-on pulse at the high-voltage transistor 430 varies with the offset voltage. The saturation behavior of the high-voltage transistor is reflected in the drain current values over the offset voltage (see for example FIG. 4).
The total voltage (cf. (Ug) in FIG. 4) results from the potential difference between the primary-side ground reference potential and the secondary-side voltage supply (Vs). Consequently, this corresponds to the sum of the offset voltage between primary and secondary side and the secondary-side operating voltage.
What is not appreciated by the related art is that in this described form of the integrated circuit configuration for actuating power switches no possibility exists, including in the simplest configuration for the secondary side of the TOP switch, for error feedback to the primary side.
Accordingly, there is a need for an improved and a preferably monolithically integrated circuit configuration for power semiconductor switches in bridge configuration as well as an associated method, which permits a primary side detection of the switched state of at least one power semiconductor switch of a secondary side by means of simple and integratable means.